feat: Room.dark + Item.light flags and Light helper

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/src/test/java/thb/jeanluc/adventure/game/LightTest.java

@@ -0,0 +1,63 @@
+package thb.jeanluc.adventure.game;
+
+import org.junit.jupiter.api.Test;
+import thb.jeanluc.adventure.io.TestIO;
+import thb.jeanluc.adventure.model.Player;
+import thb.jeanluc.adventure.model.Room;
+import thb.jeanluc.adventure.model.item.PlainItem;
+import thb.jeanluc.adventure.model.item.SwitchableItem;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class LightTest {
+    private GameContext ctx(Player p) {
+        return new GameContext(null, p, new TestIO());
+    }
+
+    private SwitchableItem lamp(boolean on) {
+        return SwitchableItem.builder().id("lamp").name("Lamp").description("d")
+                .state(on).onText("on").offText("off").light(true).build();
+    }
+
+    @Test
+    void litRoomIsAlwaysLit() {
+        Room bright = new Room("r", "R", "d"); // dark defaults to false
+        assertThat(Light.isLit(ctx(new Player(bright, 0)), bright)).isTrue();
+    }
+
+    @Test
+    void darkRoomNeedsActiveLight() {
+        Room dark = new Room("r", "R", "d");
+        dark.setDark(true);
+        Player p = new Player(dark, 0);
+        GameContext ctx = ctx(p);
+        assertThat(Light.isLit(ctx, dark)).isFalse();
+
+        p.addItem(lamp(false));
+        assertThat(Light.isLit(ctx, dark)).isFalse();   // lamp off
+
+        p.removeItem("lamp");
+        p.addItem(lamp(true));
+        assertThat(Light.isLit(ctx, dark)).isTrue();    // lamp on, carried
+        assertThat(Light.carryingLight(ctx)).isTrue();
+    }
+
+    @Test
+    void litLampLyingInRoomLightsIt() {
+        Room dark = new Room("r", "R", "d");
+        dark.setDark(true);
+        dark.addItem(lamp(true));
+        Player p = new Player(dark, 0);
+        assertThat(Light.isLit(ctx(p), dark)).isTrue();
+        assertThat(Light.carryingLight(ctx(p))).isFalse(); // not carried
+    }
+
+    @Test
+    void nonLightItemDoesNotLight() {
+        Room dark = new Room("r", "R", "d");
+        dark.setDark(true);
+        Player p = new Player(dark, 0);
+        p.addItem(PlainItem.builder().id("rock").name("Rock").description("d").build());
+        assertThat(Light.isLit(ctx(p), dark)).isFalse();
+    }
+}